This study will address the central hypothesis that the synaptic physiology (MBs) of the Mushroom Bodies underlies the temporal coding that is essential for chemosensory learning of Drosophila. The MBs have been shown to be essential for associative olfactory learning. This study will utilize a living, whole-fly preparation that allows direct pharmacological manipulation of the MBs. [Ca2+]i and membrane potential of the entire MB neuronal population will be monitored simultaneously by fluorescent imaging via a window cut in the fly's head capsule. Potentiometric dyes will be used for membrane potential imaging while new, endogenous sensors (cameleon and camgaroo mutants) will be used for Ca2+ imaging. The pharmacology relevant to the processing of chemosensory information will be investigated. The effects of acetylcholine, dopamine, octopamine, GABA, serotonin, and a putative neuropeptide gene product from the memory mutant amnesiac will be tested. The novel neurotransmitters nitric oxide and carbon dioxide will also be tested. Any secondary messenger systems thought to be involved will also be investigated. This will add to our knowledge of how neuronal systems process and encode sensory information both for perception and memory formation through learning. The broader impacts of this study are many. These imaging studies are easier to implement than electrophysiological techniques so that undergraduate seniors and graduate students can be trained to use this model for student projects that will contribute to this research. Eastern New Mexico University is a Hispanic-serving institution, as designated by the Department of Education, and it is expected that minority students will be trained and contribute to this work. Imaging, especially of endogenous sensors, is a new and exciting research tool that has yielded much useful information concerning the function of neuronal populations. Any research that contributes to our understanding of learning and memory will have an impact on the health of society.